This invention relates generally to an improved seal assembly for a centrifugal fan and more particularly to a fan with a rotating shroud that extends into a fan inlet to create a labyrinth seal.
Centrifugal fans draw air in centrally and discharge air radially. The fans can be used to provide a cooling flow for various mobile machine systems, including a heat exchanger, for example. Centrifugal fans typically have a housing and an impeller with a plurality of rotating blades that are used to generate the centrifugal airflow. A fan inlet with a fixed inlet shroud is used to direct air toward the center of the rotating blades.
In known centrifugal fans, the fan inlet is mounted to the housing and remains stationary as the impeller rotates. The performance of the fan is strongly impacted by the ability to seal the area between the impeller and the fan inlet shroud. The impeller draws air through the fan inlet and adds energy to the airflow by accelerating the flow to a high velocity. Thus, the air inside the housing is at a higher pressure than the air in the inlet. The performance of the sealing arrangement between the inlet and the impeller determines how much of the high-pressure discharge air will be drawn into the inlet. Leaks at the sealing area between the inlet and the impeller are detrimental because leakage reduces the output flow of the fan.
Low inlet clearances between the inlet and the rotating impeller are critical to high efficiency and low noise. These tight clearances can be provided at the blade tips by a low clearance, fixed, contoured inlet shroud, as discussed above. Optionally, the tight clearances can be provided by having a rotating shroud with an axially extending inlet ring coupled to a low clearance, fixed, inlet bellmouth. For mobile machine applications, either design allows recirculation near the rotating blades, which requires very low sealing clearances. This is costly and difficult to maintain on mobile machines, which are subject to high vibrations and shock loads.
The present invention is directed to overcoming one or more of the problems as set forth above.
One aspect of the invention is a fan assembly for a machine cooling system. The fan includes a housing mounted to a machine structure and an impeller that is mounted for rotation with respect to the housing about a fan axis. The impeller includes a plurality of rotating blades supported on at least one impeller flange. A fan inlet is mounted within the housing for directing air toward the blades. A rotating shroud extends outwardly from the impeller flange and has a shroud inlet that extends into the fan inlet to form a seal between the fan inlet and the shroud inlet. The seal prevents leakage as the rotating blades generate a centrifugal airflow for discharge through a fan outlet.
Another aspect of the invention is that it includes a method for sealing a rotating fan impeller having a plurality of rotating blades supported on an impeller flange to a stationary fan inlet. The method includes the steps of mounting the fan inlet to a machine structure, mounting the impeller for rotation with respect to the fan inlet, extending a rotating shroud outwardly from the impeller flange to define a shroud inlet that extends into the fan inlet, and forming a seal between the fan inlet and the shroud inlet to prevent leakage as the rotating blades generate a centrifugal airflow for discharge through a fan outlet.